The invention is concerned with an auxiliary power steering mechanism, especially for motor vehicles.
An auxiliary power steering mechanism of a pertinent type is known from EP 0101579 A2. In the embodiment according to FIG. 8 of that document, an electro-magnetic coupling is located between the electric motor and the steering gear. The coupling curves to separate the motor from the stearing gear when the motor is not being provided with current. A mechanism is thus obtained by means of which steering can be activated purely mechanically, if there is a current failure, without having a couple in the electric motor. However, the known device provides no assurance of proper functioning if a malfunction occurs in the torque-measuring device or in the electronic control circuit. Such a malfunction could consist of an apparent torque being sensed in the torque-measuring device and the electric motor being started although the steering wheel has not been turned. As a result, the vehicle would suddenly swerve from straight line travel.
Such a malfunctioning could consist of the steering wheel being turned in one direction while the electronic control device drives the electric motor in the opposite direction. In this case, too, the coupling would close, so that the electric motor would act fully on the steering mechanism.